1. Field of Invention
This invention related to folding hand tools in which a blade or working member pivots into an enclosing protective sheath which forms a handle when the tool is in use, especially pocket knives, and specifically to an improved device for moving and locking the blade.
2. Discussion Of Prior Art
The folding knife provides numerous advantages of safety, compactness, and convenience of carry over the straight blade. However, these advantages come at the expense of several interrelated disadvantages:
(a) Difficulty of deployment. The insertion of a fingernail or a pinch grip on the blade spine, and subsequent manipulation of the blade into an open position is difficult at best. If the hands are cold, wet, or slippery, then blade extraction--especially against the pressure of a backspring--becomes infeasible. PA1 Belcher, U.S. Pat. No. 23,975 (1859) PA1 Minter, U.S. Pat. No. 543,943 (1895) PA1 Schmachtenberg, U.S. Pat. No. 553,430 (1896) PA1 Papendall, U.S. pat. No. 689,513 (1900) PA1 Romano, U.S. Pat. No. 947,980 (1910) PA1 Sibley, U.S. Pat. No. 1,478,260 (1922) PA1 Grille, German U.S. Pat. No. 1,104,386 (1961) PA1 Yunes, U.S. Pat. No. 4,612,706 (1986)
(b) Two hands are required to open the blade. If one hand is unavailable, the remaining hand cannot open and deploy the blade unassisted.
(c) Strength of blade attachment. Blades are commonly attached to handles by a single pivot, which, in conjunction with whatever handle portion serves to limit their extent of opening, bears the entire working stress of the blade. Moreover, backspring and backlocking mechanisms generally preclude the use of through pins or rivets int he area of the blade pivot, which could otherwise maximize the strength of the pivot area--since this is precisely the area a spring or lever needs to move in.
(d) Blade security. Many persons feel that even the heaviest backspring pressure feasible to still allow a blade to open is insufficient to insure against accidental collapse of the blade. Many different types of blade locking devices, and knives in which the blade is positively locked against accidental closure, have been devised. Most designs gain locking security at the expense of convenience or strength.
(e) Blade wobble. Related to the previous factor. Manufacturing allowances must be provided so that parts can move freely. But in a folding knife this may result in mechanical looseness which is perceived as blade wobble. manufacturers commonly reduce perceived wobble in backspring knives by increasing backspring pressure. This makes such knives hard to open.
Some efforts to minimize or overcome these disadvantages are of particular interest:
My own U.S. pat. No. 4,974,323 (1990) disclosed a folding knife or tool in which the blade is moved and locked by an integral control piece, which appears as a stem or button on the handle and a flat portion of which si moved within a cavity in the handle to position a crankpin on the blade tang. This design resolved for the first time the above mentioned problems. It provides total blade movement and locking control with a single button on the handle. However, despite the success of this design, some persons lack the manual dexterity to operate the knife easily. This difficulty is believed to relate to the eccentric movement of the control member, which requires that the finger change direction just at the point of least mechanical advantage.
An additional difficulty for these users is that the locking and unlocking operations require a separate and distance control movement from that used to move the blade.
Many users, therefore, would find it desirable to have a knife or folding tool which embodies a simplified means for achieving safe and effective one hand control of blade movement and locking, and which provides a constant leverage on the blade over the total path of the control member movement, and automatic locking of the blade at the open and closed positions.